1. Field of the Invention The present disclosure relates to a method for depositing a silicon nitride film.
2. Description of the Related Art
Japanese Patent Application Publication No. 2012-138501 discloses a trench filling method that includes steps of forming an oxide barrier layer inside a trench formed in a semiconductor substrate, forming an expandable film on the oxide barrier layer, and filling the trench with a filling material which contracts by being fired. In the method, the step of forming the oxide barrier layer includes steps of forming a first seed layer inside the trench, and forming a silicon nitride film on the first seed layer, and the step of forming the expandable film on the oxide barrier layer includes steps of forming a second seed layer on the silicon nitride film, and forming a silicon film on the second seed layer.
The trench filling method disclosed in Japanese Patent Application Publication No. 2012-138501 enables the expandable film and the oxide barrier layer to be formed inside the trench even if miniaturization of trenches further develops.
However, in some cases, processes require filling a recess such as a fine trench for wiring with a silicon nitride film with preferable filling characteristics without generating a void, not with the expandable film as disclosed in Japanese Patent Application Publication No. 2012-138501. In such cases, just filling the recess with a film so as to conform to a shape of the recess may be insufficient, and the recess may not be preferably filled up with the silicon nitride film unless the silicon nitride film gradually fills the recess while maintaining a V-shaped cross section so as not to close the opening of the recess. In other words, because the recess is very fine, even if the film is intended to be deposited so as to conform to the surface of the recess, the film may close the opening of the recess while leaving a void in a middle portion of the recess. In such film deposition, generation of the void cannot be prevented unless the recess is gradually filled with the film while maintaining a V-shaped opening cross-section in the film as discussed above.